1. Field of the Invention
The present invention relates to light trigger type semiconductor devices, and particularly to an improvement for enhancing the transmission efficiency of light signals.
2. Description of the Background Art
FIG. 9 is a front sectional view showing an example of a light activated thyristor (a light trigger type thyristor) of the pressure welding type. As shown in FIG.9, in this light activated thyristor, a thermal compensating plate 3 formed of material having its coefficient of thermal expansion approximate to that of a semiconductor substrate 1 is attached to the lower main surface of the semiconductor substrate 1 having the thyristor elements built therein. This thermal compensating plate 3 and the semiconductor substrate 1 are soldered to each other with solder material such as aluminum or aluminum-silicon.
The thermal compensating plate 3 is subjected to the shaping processing at its end surface, and also subjected to the chemical treatment, and further, the surface treatment agent is applied thereto. A main electrode 5 formed of copper abuts on the lower main surface of the thermal compensating plate 3. This main electrode 5 is silver-soldered to an insulation tube 6 formed of ceramics through a metal plate 8.
Another thermal compensating plate 2 is provided on the upper main surface of the semiconductor substrate 1. This thermal compensating plate 2 is made to adhere to the upper main surface of the semiconductor substrate 1 with silicone rubber, for example. A main electrode 4 formed of copper abuts on the upper main surface of the thermal compensating plate 2. The main electrode 4 is silver-soldered to the insulation tube 6 formed of ceramics through a metal plate 7.
The insulation tube (outer surround) 6 establishes insulation between the two main electrodes and forms a housing accommodating the semiconductor substrate 1 and the like inside together with the main electrodes 4, 5 and the metal plates 7, 8. A metal tube 11a for guiding light signals and a metal tube 11b functioning as an exhaust spigot are attached to the insulation tube 6 by silver soldering.
A light guide 10 for guiding the light signals inputted from outside to a light receiving portion is inserted in the metal tube 11a. This light guide 10 airtightly adheres to the metal tube 11a with an adhesive agent such as solder or glass with low melting point. The light receiving portion 1a is provided at the center part of the semiconductor substrate 1, to which the light emitting end of the light guide 10 is fixedly coupled.
The light guide 10 and the light receiving portion la are bonded by using an optical coupling agent 21 such as silicone rubber or the like which has optical transparency, refractive index approximate to that of the light guide 10, and buffering effect. The light guide 10 is fixed to prevent a decrease of the coupling efficiency of the optical transmission system to transmit optical power as large as possible to the light receiving portion 1a.
The inside of the above-described housing is made airtight, and inert gas is sealed therein. With the semiconductor substrate 1, the thermal compensating plate 2, and the thermal compensating plate 3 accommodated in the housing, the end surface of the metal plate 8 silver-soldered to the main electrode 5 and the insulation tube 6 are finally welded, and the gas remaining inside is exhausted through the metal tube 11b and replaced by inert gas, and then the end portion of the metal robe 11b is arc-welded to realize the airtightness of the housing and seal of the inert gas.
The light signal is transmitted through an external optical fiber (not shown) from an external LED, LD, etc. (not shown), which serves as a light source, and then guided to the light entering end of the light guide 10 through an external connector (not shown). The light guide 10 changes the direction of progress of the incident light signal by 90.degree. and irradiates the light receiving portion 1a from the light emitting end facing to the light receiving portion 1a of the semiconductor substrate 1.
The semiconductor substrate 1 converts the light signal into the photoelectric current in the vicinity of the light receiving portion 1a and amplifies the photoelectric current to establish a conductive state between the two main electrodes 4 and 5. That is to say, this device performs switching operation triggered by the light signals.
As the conventional semiconductor device is constructed as described above, loss occurs in the respective transmission elements and at connections among the elements while light signals are transmitted from the light source to the light receiving portion 1a of the semiconductor device, resulting in a problem that the sensitivity of the device is low. To decrease the loss has been one of the important problems of the light trigger type semiconductor devices.